1. Field of the Invention
The present invention relates to a camera having a zooming mechanism and, more specifically, it relates to an auto focus camera with a zoom lens unit to the front end of which a converter for variable focal length can be attachable.
2. Description of the Prior Art
Conventionally, when a lens for variable focal length such as a converter is attached to the front side of a zoom lens unit, the position of a variator for the zoom lens unit is not changed before and after the attachment of the converter. For example, if we use a 6 times zoom lens unit with the focal length of 9 mm to 54 mm as a zoom lens unit, and attach a teleconverter of 1.5 magnification rate, the focal length will be only about 45 mm when the focal length is set at 30 mm directly before the attachment of the converter.
In that case, the attachment of the teleconverter has no considerable effect. The effect of the attachment of the teleconverter is maximized when the converter is attached with the variator of the zoom lens unit set at an end of a telephoto range (hereinafter referred to as the tele end). Therefore, a photographer must move the variator of the zoom lens unit to the tele end before the attachment of the teleconverter or he must move the variator to the tele end after the attachment of the teleconverter. The same problem occurs when a wide converter is attached.
Meanwhile, in attaching a converter in front of the zoom lens unit, the converter of a large diameter has been used in order that portions of the beam is not shaded by the converter. Particularly, in attaching a converter in front of a zoom lens unit, the light path changes along with the movement of the variator, so that a converter should be prepared which is designed not to shade the light path in the entire zooming range. In that case, the diameter of the converter will be still larger.
The converter having a lens of such large diameter is large-sized and has considerable weight. Therefore, even if the zoom lens unit is made compact, the camera as a whole will be very large when such converter is attached thereto. On the contrary, if a small and light converter is attached, shading may occur as described above, or sufficient compensation cannot be provided by a compensator. More specifically, afocal design may be employed for a teleconverter for zooming, however, in that case shading sometimes occurs in a portion of a zooming range defined by the movement of the variator, if the converter is made with small diameter in order to make it compact. Afocal designed wide converter has a large diameter, so that a camera as a whole will be large-sized when the same is attached to the camera. On the other hand, although a wide converter which is not afocal designed is compact, the necessary moving amount of the compensator corresponding to the zoom amount will be extremely large and the compensation by a compensator becomes substantially difficult.